fread2: Fast and friendly file finagler
In privefl/kaggler: What the Package Does (One Line, Title Case)

Similar to read.table but faster and more convenient. All controls such as sep, colClasses and nrows are automatically detected. bit64::integer64 types are also detected and read directly without needing to read as character before converting.

Dates are read as character currently. They can be converted afterwards using the excellent fasttime package or standard base functions.

'fread' is for regular delimited files; i.e., where every row has the same number of columns. In future, secondary separator (sep2) may be specified within each column. Such columns will be read as type list where each cell is itself a vector.

1	fread2(...)

...

Arguments passed on to data.table::fread

input: Either the file name to read (containing no \n character), a shell command that preprocesses the file (e.g. fread("grep blah filename")) or the input itself as a string (containing at least one \n), see examples. In both cases, a length 1 character string. A filename input is passed through path.expand for convenience and may be a URL starting http:// or file://.
sep: The separator between columns. Defaults to the first character in the set [,\t |;:] that exists on line autostart outside quoted ("") regions, and separates the rows above autostart into a consistent number of fields, too.
sep2: The separator within columns. A list column will be returned where each cell is a vector of values. This is much faster using less working memory than strsplit afterwards or similar techniques. For each column sep2 can be different and is the first character in the same set above [,\t |;:], other than sep, that exists inside each field outside quoted regions on line autostart. NB: sep2 is not yet implemented.
nrows: The number of rows to read, by default -1 means all. Unlike read.table, it doesn't help speed to set this to the number of rows in the file (or an estimate), since the number of rows is automatically determined and is already fast. Only set nrows if you require the first 10 rows, for example. 'nrows=0' is a special case that just returns the column names and types; e.g., a dry run for a large file or to quickly check format consistency of a set of files before starting to read any.
header: Does the first data line contain column names? Defaults according to whether every non-empty field on the first data line is type character. If so, or TRUE is supplied, any empty column names are given a default name.
na.strings: A character vector of strings which are to be interpreted as NA values. By default ",," for columns read as type character is read as a blank string ("") and ",NA," is read as NA. Typical alternatives might be na.strings=NULL (no coercion to NA at all!) or perhaps na.strings=c("NA","N/A","null").
file: File path, useful when we want to ensure that no shell commands will be executed. File path can also be provided to input argument.
stringsAsFactors: Convert all character columns to factors?
verbose: Be chatty and report timings?
autostart: Any line number within the region of machine readable delimited text, by default 30. If the file is shorter or this line is empty (e.g. short files with trailing blank lines) then the last non empty line (with a non empty line above that) is used. This line and the lines above it are used to auto detect sep, sep2 and the number of fields. It's extremely unlikely that autostart should ever need to be changed, we hope.
skip: If 0 (default) use the procedure described below starting on line autostart to find the first data row. skip>0 means ignore autostart and take line skip+1 as the first data row (or column names according to header="auto"|TRUE|FALSE as usual). skip="string" searches for "string" in the file (e.g. a substring of the column names row) and starts on that line (inspired by read.xls in package gdata).
select: Vector of column names or numbers to keep, drop the rest.
drop: Vector of column names or numbers to drop, keep the rest.
colClasses: A character vector of classes (named or unnamed), as read.csv. Or a named list of vectors of column names or numbers, see examples. colClasses in fread is intended for rare overrides, not for routine use. fread will only promote a column to a higher type if colClasses requests it. It won't downgrade a column to a lower type since NAs would result. You have to coerce such columns afterwards yourself, if you really require data loss.
integer64: "integer64" (default) reads columns detected as containing integers larger than 2^31 as type bit64::integer64. Alternatively, "double"|"numeric" reads as base::read.csv does; i.e., possibly with loss of precision and if so silently. Or, "character".
dec: The decimal separator as in base::read.csv. If not "." (default) then usually ",". See details.
col.names: A vector of optional names for the variables (columns). The default is to use the header column if present or detected, or if not "V" followed by the column number.
check.names: default is FALSE. If TRUE then the names of the variables in the data.table are checked to ensure that they are syntactically valid variable names. If necessary they are adjusted (by make.names) so that they are, and also to ensure that there are no duplicates.
encoding: default is "unknown". Other possible options are "UTF-8" and "Latin-1". Note: it is not used to re-encode the input, rather enables handling of encoded strings in their native encoding.
quote: By default ("\""), if a field starts with a doublequote, fread handles embedded quotes robustly as explained under Details. If it fails, then another attempt is made to read the field as is, i.e., as if quotes are disabled. By setting quote="", the field is always read as if quotes are disabled.
strip.white: default is TRUE. Strips leading and trailing whitespaces of unquoted fields. If FALSE, only header trailing spaces are removed.
fill: logical (default is FALSE). If TRUE then in case the rows have unequal length, blank fields are implicitly filled.
blank.lines.skip: logical, default is FALSE. If TRUE blank lines in the input are ignored.
key: Character vector of one or more column names which is passed to setkey. It may be a single comma separated string such as key="x,y,z", or a vector of names such as key=c("x","y","z"). Only valid when argument data.table=TRUE.
showProgress: TRUE displays progress on the console using \r. It is produced in fread's C code where the very nice (but R level) txtProgressBar and tkProgressBar are not easily available.